大厦表达式树 [英] Building Expression Trees

问题描述

我和如何建立更多的lambda表达式树的想法挣扎，如一个下面，更不用说一些可能有多个语句。例如：

I'm struggling with the idea of how to build an expression tree for more lambdas such as the one below, let alone something that might have multiple statements. For example:

Func<double?, byte[]> GetBytes
      = x => x.HasValue ? BitConverter.GetBytes(x.Value) : new byte[1] { 0xFF };

我将不胜感激的任何想法。

I would appreciate any thoughts.

推荐答案

我建议通过方法阅读列表在表达类，所有的选项都列出，并 。表达式树编程指南

I would suggest reading through the list of methods on the Expression class, all of your options are listed there, and the Expression Trees Programming Guide.

对于此特定实例：

/* build our parameters */
var pX = Expression.Parameter(typeof(double?));

/* build the body */
var body = Expression.Condition(
    /* condition */
    Expression.Property(pX, "HasValue"),
    /* if-true */
    Expression.Call(typeof(BitConverter),
                    "GetBytes",
                    null, /* no generic type arguments */
                    Expression.Member(pX, "Value")),
    /* if-false */
    Expression.Constant(new byte[] { 0xFF })
);

/* build the method */
var lambda = Expression.Lambda<Func<double?,byte[]>>(body, pX);

Func<double?,byte[]> compiled = lambda.Compile();

这篇关于大厦表达式树的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！